1. Field of the Invention
The present invention relates to a structure mainly applying a localized plasmon resonance phenomenon, a method of manufacturing the structure and a sensor using the same, and more particularly to a technique for arranging metallic particles for inducing a plasmon resonance at a high density.
2. Description of the Related Art
Referring to a metal dot, such as formed by gold or silver with a smaller size being smaller than the wavelength of light, occurring a localized plasmon resonance is well known, and a device making use of said phenomenon is also known. Forming a metal colloid monolayer film is known as a method of forming such a device. For example JP-A2000-356587 has disclosed one of the utilizations of the properties. In this publication, metallic particles are fixed like a film on the surface of a substrate formed by an optional material such as a dielectric, a metal or a semiconductor and are thus used as a sensor unit, and light is irradiated on the sensor unit to measure the absorbance of the light transmitted through the metallic particles fixed to the substrate. Consequently, the refractive index of the medium in the vicinity of the surface of the metallic particles fixed to the substrate, for example, at a distance which is almost equal to the diameter of the metallic particle is obtained Thus, the detection of the adsorption and deposition of a substance onto the metallic particles in the sensor unit can be carried out.
In this case, the sensor unit is constituted by forming a metal colloid monolayer film by metallic particles having a diameter of approximately 10 to 20 nm on a substrate formed of glass. The metal colloid monolayer film is fabricated by immersing the substrate formed of glass in a 10% methanol solution of 3-aminopropyltriethoxysilane for 10 minutes, washing the substrate, and furthermore, immersing the substrate in a solution of metal colloid having a diameter of approximately 20 nm for two hours.
In the conventional sensor, however, a metal colloid monolayer film is formed and a large number of metallic particles are thus fixed onto the substrate. Therefore, the monolayer film can suitably be formed in a state in which the metallic particles are not condensed but isolated from each other. However, it is hard to carry out fabrication with the metallic particles having a uniform size and to regularly arrange the metallic particles.
More specifically, concerning the applicability to the sensing devices for detecting change made to the refractive index, the resonance condition being influenced by dispersion of the particle sizes or their shapes is the problem to be concerned as disclosed in the related art such as “Metal Nanoparticle, 89” by Daniel L. Feldheim and Colby A. Foss, Jr. Therefore, in case of such dispersion being not controllable, it brings about lowering the sensitivity because resonance-caused absorption or resonance wave length are also dispersed accordingly.
As an example, description will be given to the related art in which a thin poly(methyl methacrylate) (PMMA) film is deposited on the metallic particle 7 formed of gold fixed to the base material 11. In flus case, the absorbance of a resonance peak is increased and shifted toward the long wavelength side when the thickness of the thin PMMA film thus deposited is increased as shown in a result obtained by measuring the relationship between the wavelength and the absorbance for each thickness of the thin film in FIG. 4.
Further, when dispersion in the sizes or the shapes are occurring over a plurality of the sensing devices, it raises another problem, namely difficulty for determining whether the measured absorbance or resonance wave length are obtained from changes made in refractive index, or said dispersion in the sizes or the shapes, which might end up lowering its reliability of the sensing devices. The conventional choroids-used method, being known for forming metal particles, results in dispersion having ±6.6% even with its best mode as reported in the above mentioned “Metal Nanoparticle, 89”. However, its range might be further enlarged through the conventional manufacturing process, such as to ±10% or so as reported in “Optical letters 25,6,372 (2000)” by Takayuki Okamoto. For the reasons mentioned above, a method for controlling dispersion of the particle sizes or their shapes has been expected.